This proposal is focused on developing glucan particles (GPs) as a novel vaccine platform and adjuvant that promotes protective T cell and antibody responses. GPs are hollow, highly purified yeast cell walls composed predominantly of -1,3-glucan. Preliminary studies demonstrate robust and long-lasting adaptive T cell and antibody responses following immunization of mice with GPs loaded with antigen. Moreover, mice vaccinated with GPs containing antigen from Histoplasma capsulatum (Hc) survive otherwise lethal experimental histoplasmosis. The experiments will address the central hypothesis that antigen-loaded GPs make effective vaccine platforms by alerting the immune system to the presence of danger, directing antigens into DCs and stimulating protective adaptive T and B cell responses. It is further hypothesized that the immune response can be beneficially manipulated by the addition to the GP platform of other adjuvants, such as TLR agonists and siRNA targeting negative regulators of inflammation. Aim 1 is to decipher the afferent pathways stimulated by GPs that shape T cell and antibody responses. The hypothesis to be tested is administration of GPs containing encased Ag results in complement activation, uptake by DCs via complement receptors and Dectin-1, migration of DCs containing GPs to draining lymph nodes and stimulation of a robust adaptive immune response including antibody and Th1/Th17-biased CD4+ T cell responses. Aim 2 is to investigate the efferent mechanisms by which fungal antigens complexed in GPs protect against Hc infection in mice. The hypothesis to be tested is uptake of antigen-bearing GPs by DCs shapes the immune response to generate a protective Th1 and/or Th17 response. Aim 3 is to explore novel approaches to boosting the immunogenicity of the GP platform. The hypothesis to be tested is the capacity of GP-formulated vaccines to protect against challenge with Hc can be augmented by specific stimulators of the innate immune response. We anticipate that at the end of the funding period, we will have created GP-based vaccines using FDA- approved materials capable of eliciting robust and durable antibody and Th1-/Th17-biased responses that protect immunocompetent and immunocompromised mice against challenge with Hc. Moreover, we anticipate that by altering the composition of the vaccines (such as by the addition of TLR ligands or siRNA), we will positively impact the nature of the responses. The studies address an NIH-identified need for development of a vaccine to protect immunocompromised and immunocompetent individuals in endemic regions from histoplasmosis. In addition, the studies should establish a proof of principle regarding the efficacy of GP-based vaccine platforms that should be applicable to other vaccine-preventable diseases and form the basis for eventual testing in humans.